The present invention is directed toward a rotary actuator that utilizes a shape memory alloy as an operative component thereof.
Various types of devices have been proposed that utilize a heat recoverable metal, such as Nitinol, as an operative component of the device. Nitinol is an electrically conductive alloy containing large proportions of nickel and titanium. A Nitinol wire, for example, may be stretched up to about 10% of its length and will remain in the stretched state even when the tensile stress used to stretch the wire is removed. If the temperature of the wire is then elevated above its martensitic critical temperature, the wire will return to its original unstretched state as if it has a "memory" of it unstretched length.
When the wire contracts to its original length it exerts a contracting force which has been used in various applications. Co-pending U.S. patent application Ser. No. 946,480 discloses a gripping device wherein linear actuation is provided by the contracting force of the Nitinol wire. U.S. Pat. No. 4,002,954 discloses the utilization of a Nitinol wire for activating a photographic shutter and sets forth a particular electronic circuit arrangement to provide a current pulse sufficient to heat the Nitinol wire to the critical temperature. U.S. Pat. Nos. 3,740,839 and 4,497,527 disclose connecting devices utilizing a socket member with several tines and a band positioned over the tines for biasing them toward their center in a contracted state of the band. The band is made of a heat recoverable metallic material. Additional teachings of heat shrinkage and heat recoverable material may be found in U.S. Pat. Nos. 3,445,898, 3,622,941 and 4,556,050.